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Orthorectifying GeoEye-1 Data Rigorous and RPC Modeling

GeoEye–1, launched on September 06, 2008 is the highest resolution commercial earth imaging satellite available till date. GeoEye-1 has capability to simultaneously acquire 0.41 m panchromatic imagery and 1.65 m multispectral imagery. The highly detailed and geospatially accurate GeoEye-1 imagery can be utilized in any market segment. Data is distributed by GeoEye (www.geoeye.com).

The following is a brief tutorial over the use of Geomatica OrthoEngine v10.2 for Orthorectifying GeoEye-1 Geo-Ortho ready data (Geo Ortho Kit) with the Rigorous Model and Rational Polynomial Coefficients (RPC).

Rigorous Modeling - Initial Project SetupStart OrthoEngine and click ‘New’ on the File menu to start a new project. Give your project a ‘Filename’, ‘Name’ and ‘Description’. Select ‘Optical Satellite Modeling’ as the Math Modeling Method. Under Options, select ‘Toutin's Model’. After accepting this panel you will be prompted to set up the projection information for the output files, the output pixel spacing, and the projection information of GCPs. Enter the appropriate projection information for your project.

Data InputFor Rigorous Modeling with Geomatica OrthoEngine, the user should have GeoEye-1 “Basic” or “Geo” product. GeoProfessional and GeoStereo products are pre-processed to a further extent than Geo product. Since they have a correction already applied, therefore GeoProfessional and GeoStereo imagery products cannot be Orthorectified. For more information on these products, please refer to GeoEye-1 official website www.geoeye.com

Select ‘Data Input’ option from ‘Processing Step’ drop down and click on ‘Read CD-ROM data’ button (Please note that we are treating this data as if it is on CD-ROM, even though it is actually located on the hard disk)

Choose ‘IKONOS, GeoEye_Geo’ as the ‘CD Format’ and select your TIFF or NITF image file. Press the appropriate channel buttons (1 for a PAN image). Specify an appropriate output ‘PCIDISK filename’, a ‘Scene description’, and a ‘Report filename’. This step will convert the source file to ‘.pix’ format, and add the orbital information needed for modeling.

For the GeoEye-1 Rigorous model, a minimum of six accurate GCPs per image (or more, depending on the accuracy of the GCPs and accuracy requirements of the project) are required. After collecting the GCPs, select the ‘Model Calculation’ Processing Step and click on ‘Compute Model’. Check ‘Residual Report’ panel (under the Reports processing step) to review the initial results.

Generating OrthosThe final step is to set up your Ortho Image Production. Proceed to the ‘Ortho Generation’ processing step and select the file(s) to be orthorectified. Choose the DEM file to be used in the processing and other processing parameters. Click on ‘Generate Orthos’ to create the final Orthorectified image.

Rational Polynomial Coefficients (RPC)GeoEye-1 Geo Ortho-Kit data is delivered with RPCs, which can be used in the absence of adequate GCPs. Further addition of 1-4 GCPs into your project, in addition to the delivered RPCs can significantly improve the accuracy of your final Orthophoto.

Merge/PANSHARP Multispectral ImagesFor the GeoEye-1 Geo-Ortho Kit the panchromatic and multispectral images are resampled exactly on top of each other. Therefore, it is possible to perform pansharpening of the data first, for gentle terrain before further processing. Thus, you need to perform GCP collection and orthorectification only once to the pansharpened image.

This process will generate a PIX and a RPC file. After the successful completion, software will prompt to add the pansharped image to the project. Select ‘OK’ to continue with the project.

Review CoefficientsCoefficients can be reviewed by using ‘Project Report’ option under the ‘Reports’ processing step. Select ‘Geometric Model’ under Image Information panel.

GCP CollectionAt this stage an Orthophoto can be directly generated in the absence of any GCPs. The model will be computed based on the supplied RPCs.If GCPs are available, they can be added into the project using GCP/TP Collection option. The model can be automatically computed (using Compute Model option), and GCPs can be reviewed through Residual report.

Ortho GenerationThe final step is to ‘Schedule Ortho Generation’. Proceed to the ‘Ortho Generation’ processing step and select the files to be processed. Select an appropriate DEM file and set other processing options before generating the final Orthophoto.